A conventional throttle body includes a bore, a throttle valve, mechanical linkage for actuating the valve, a throttle position sensor and possibly an idle air control actuator responsible for smoothing out the air flow during idle operation. In systems having electronic throttle control, the idle air control function may be performed directly by the electronic throttle control, eliminating the idle air control actuator. To obtain the necessary accuracy in positioning and motion of the valve by an electronic throttle control actuator, the bore of the throttle body or air control valve may be shaped. For example, a spherical shape may be applied to the bore either above or below the valve to block air flow on half the bore for an initial angular rotation of about 10 to 22 degrees. For large bore throttle bodies and normal air flow resolution requirements this is a feasible solution. However, for smaller bores and more precise air flow requirements, a single spherical shape will not produce sufficiently fine air flow resolution (small enough increments of air flow change) to meet idle air flow requirements using a current electronic throttle control actuator. One solution would be to provide a special actuator with finer control steps, at least in the idle range; however, further modification of the throttle body bore could be a more economical solution.